The field of the present invention is actuator valves for air driven reciprocating devices, and more specifically wherein the valve includes a pneumatically controlled valve piston.
Actuator valves for reciprocating pneumatically driven devices have been developed which employ a pilot valve or rod responsive to the position of the reciprocating element of the device and a pneumatically controlled valve piston responsive to the position of the pilot rod. The valve piston in turn controls the incoming flow of pressurized air to provide an alternating flow to the reciprocating device. This alternating flow forces the device to stroke back and forth thereby performing work and driving the pilot rod. Such actuator valves thus convert a relatively steady source of pressurized air into an alternating flow without need for any outside timing or control system. The source air pressure alone drives the valve as well as the working device.
One such actuator valve used primarily on air driven diaphragm pumps is disclosed in U.S. Pat. No. 3,071,118, the disclosure of which is incorporated herein by reference. Such air driven diaphragm pumps include diaphragms positioned on either side of an actuator valve in an arrangement similar to that set forth in the present figures, outwardly of the actuator valve and pilot or control rod. Such additional devices and configurations are illustrated in U.S. Pat. No. 4,242,941, No. 4,247,264, No. 4,339,985 and No. Des. 268,413, the disclosures of which are incorporated herein by reference.
The shifting of the valve piston in such devices is understood to occur by the selective venting of one end of the enclosing cylinder in which the piston moves. By selectively venting one end or the other of the cylinder, the energy stored in the form of compressed air at the unvented end of the cylinder acts to drive the piston to the alternate end of its stroke. Under proper conditions, the energy is more than sufficient to insure a complete piston stroke. However, under adverse conditions, such as when foreign material, dirt, grease and the like, is allowed to collect within the cylinder, the damping or resistance to movement of the piston may so increase that the system may require all available potential energy for shifting of the piston. Under such marginal conditions, all possible energy is advantageously applied to insure operation of the actuator valve. One mechanism for providing additional energy for shifting is presently included in the devices of the aforementioned patents. Additional compressed air is supplied through passageways to the expanding chamber at one end of the valve piston. The air is gated into the passageways by the location of the piston. Additional energy, however, could also be useful under severe conditions.
The nature of air driven reciprocating devices such as contemplated for use with the present actuator valve gives them the ability to be used on demand by simply stalling the device rather than by shutting off the source of compressed air. Such a condition might exist with an air driven diaphragm pump where the product to be pumped is maintained under pressure and controlled downstream of the pump by a valve. When the valve is opened, the pump is able to move material through the pump and through the valve. When the valve is closed, the pump will stall when the driving air force equals the compression force on the material being driven. Under such conditions, the pump remains ready to pump further material at any time that the downstream valve is opened.
When an air driven reciprocating device is employed in this manner, the actuator valve will simply remain in the position at the time of stall. Under such conditions virtually no air is used to maintain the pump. However, any passages open to atmosphere and also connected to the inlet pressure will continue to allow air flow therethrough. Therefore, it is advantageous to avoid any point in the pump or actuator valve stroke when such leakage can occur. Any such leakage can be noisy and esthetically unpleasing even if it is not sufficient to amount to a noticeable loss of compressed air.